This project will test the hypothesis that Attention Deficit Hyperactivity Disorders (ADHD) are related to abnormalities of frontal networks involving the frontal lobes, basal ganglia and cerebellum. Three main approaches will be used: 1. Neurobehavioral tests to examine this system, specifically response inhibition, Motor impersistence, visual habituation, motor and perceptual timing. 2. Volumetric MRI with focus on frontal lobes, basal ganglia and cerebellum. 3. Functional MRI aimed to evaluate frontal cortex and basal ganglia activation during the performance of a task involving response inhibition. Forty children between the ages of 8 & 12 years who meet the currently agreed upon criteria for ADHD, will be recruited from various sources in our local community, and compared with a control population from community peeers, referred to as the "snowball" technique which has been used in previous published studies.